A billet in the sense of the present invention is in particular a metallic wire which has an integrally-formed cross-sectional area perpendicular to its longitudinal axis or a bundle of such metallic wires.
Subsequent to the cold processing of a metallic billet, and especially after a metallic billet has been drawn, structural changes can be observed in said metallic billet, which is also especially the case with billets made of aluminum or aluminum alloys. These structural changes in particular have an effect of hardening the billet and reducing its elongation at rupture. Such structural changes limit the uses for a billet so that a feasible measure to remedy same consists in stress-relief annealing of the billet, which induces a re-crystallization of its structure. In so doing, the billet is heated employing direct resistance heating for engineering and economic reasons. This direct resistance heating integrates a section of the billet, respectively one billet segment at a time, into an electrical circuit so that an electric current flows through said billet section or segment and, due to the electrical resistance of the billet, at least a portion of the electrical energy is converted to thermal energy, hence heating the billet.
During resistance heating, respectively annealing, the billet is guided, for example continuously, along a plurality of contact plates. Said contact plates are connected to a voltage source such that a current can flow through the metallic billet.
Considerable problems arise when current is transmitted from contact plates to billets containing aluminum or aluminum alloys. Such problems give rise to having to operate these types of devices in a cost-intensive manner and result in the quality of the annealed billet not remaining constant over time.
The inventor is additionally aware that billets made of aluminum or of an aluminum alloy are heated in furnaces (furnace or drop annealing) in batch processing. Thus, the billets supported on a metallic spool or other metallic carrier are subjected to a protective gas atmosphere in an annealing furnace for a period of several hours.
Such a process necessitates great technical production expenditures as well as being energy and cost-intensive and furthermore gives rise to extremely long passage times with high process costs and frequently inadequate product quality.
The inventor is moreover aware that in the production of rods, wire is annealed employing a consumptionsly annealing passage process based on a conductive principle, although the quality of such products is generally insufficient in this case as well.